Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave antenna. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF. Isn't it? Lets call this element the LoadAttenuator. Why had I not noticed this before? I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. Thanks again Jim. A week or two later I started to notice an occasional knocking sound inside the house. Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. I can give a link if you need. Which begs the question what happens when you attach the antenna? Most informative and appreciated. If you stare at the above frequency sweeps you will discover a few things. This is indeed a classic antenna that is not only, Introduction to Omnidirectional Antennas In the literal sense, an Omnidirectional antenna is an antenna that radiates uniformly in all directions. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. Change), You are commenting using your Facebook account. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. It is important that resonance may be achieved at each tap of the inductance. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. It performed well on both the 2m and 70cm bands. I found that sometimes the multimeter that was measuring the temperature would give unreliable information when RF was present, so the off periods provided regular intervals for measuring the temperature. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Can you give me an idea for your 100 W version, you built for 80/60/40 m. Wow, Gary! Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. This gave me an effective coil diameter of 40.5mm. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. Impressive article and so well done that I may give it a try. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. Does your station desperately need a good RF ground to behave properly? It will present its parameters, so anybody with basic home-brew skills will be able to build it. Thanks! In his article, I will try to bust some of the myths associated with Inverted. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. So far so good. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. 100W on a Wire Antenna - Is it good enough for DX? <> However, a key restriction is its 25W power rating, due to the small matching transformer. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. Let's find out! The radiation pattern of this antenna on most bands produces multiple lobes. Workers' Comp. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Very interesting design. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. Understanding Antennas The Good, the Bad, and the Ugly. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Some say you do not need a counterpoise, but that is false. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. I needed to add an additional coil (approx 12.5 uH) about . From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. 5) It is very hard to avoid stray capacitance on the output. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. I have been using a 40m End-Fed Half Wave (EFHW) antenna very successfully for the last few months and I wanted to extend the design to multi-band whilst avoiding the need to take a . Consider the RC time for a source with 2500 impedance into a 1pF capacitor. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. The negative effects of local QRM on an, How does antenna radiation occur? Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. You cant really see the antenna wire, but the red line shows the antenna path. A radio station is as good or as bad as the antenna it has. Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. The difference here is that the target bands are low frequency. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. The biggest uncertainty in these measurements was the actual power level used. We use cookies to optimize our website and our service. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. After doing the ferrite transformer scaling experiments last time, and learning a bit more about what matters in these transformers, it was time to make a stab at designing one. I found it very useful to label the tuner with switch and capacitance positions. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. View the job description, responsibilities and qualifications for this position. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. A 100pF silvered mica was connected in shunt with the transformer . One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. Low SSN Why do most Hams find HF Radio so difficult? This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. Each geodesic great circle path displayed on the map originates from your location that is derived Read More, The Great Circle Map GCM We present an automatically rendered Great Circle Map GCM based on your location derived from your Internet IP address. Loss (to mean PowerIn/PowerOut) can be calculated in dB as -|S21|-LoadAttenuator-MismatchLoss=18.64-18.16-0.03=0.450dB, or an efficiency of 10^(-0.45/10)=90.2%. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. One point of my small-core, compact winding design was to be able to cool the core. High self-resonant frequency. This will yield the maximum capacity of the variable capacitor. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Klubunknl folyamatos a tagfelvtel. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Thank you for an interesting and informative read. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. There is much more that can be written about this antenna and its matching, but that was not my aim. EFHW coil and 80m extension in place (coil visible at tip of red arrow) With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. One end is about 5 meters high on an extended fishing pole. Taking the time derivative of the above equation you get the power dissipation. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. Above is a sweep of the roughly compensated transformer. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. See the table above. I wish I had a simple answer, but really this is where some experimentation can pay off. The overall lenght is only 15m. Of course, you will need to find your tuning positions and apply your own position scale. Finally the tank circuits specification is complete, which is sown below. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Hence, there is no optimum single-fit solution. 73! Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. The highest frequency could be14.350MHz. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. I have seen and read quite a few reports of making this antenna, and some got away no problem with the 110uH when they came to set up and adjust the antenna, others needed to tweak their coil turns. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. This suggests an inductive reactance. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. Feeling brave, I decided to tape my coil up and solder connectors on and hope I would be one of the lucky ones who wouldnt need much coil adjustment (will I be right??). The overlaid VSWR plots are shown below. Note that there is some uncertainty in the measurements, but we can be confident that the loss is no where near the figure estimated for the FT82-43 design. 1. VK1OD.net (offline). I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Based on a 2014 survey, the most popular antennas for SOTA (Summit On The Air) activation are the following (see sotabeams.co.uk/blog/5-most-popular-hf-portable-antennas for details): Let us not confuse the End-Fed Half Wave antenna with the Random Length End Fed wire. These dimensions were derived from modelling the antenna in EZNEC. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en. Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency). Looking at several builds and discussions, such as commercial antennas (e.g. I then used a piece of heat shrink on the outside to hold everything in place. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave Ham Radio DX 27.1K subscribers 19K views 7 months ago #HamRadio #AmateurRadio #EFHW Here are my experiments and modifications with an EFHW. Be sure to take a look for additional analysis and conclusions. Typically the IC-751A would read about 60W on its power bridge, the Siliconix would show >50W on the 50W scale and 45W on the 500W scale, so there is ~20% uncertainty. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. I was pleasantly surprised that the dips were so perfect across all of the bands and the SWR was low enough to not really need a tuner. It is very hard to know what will be the best solution for a given antenna installation if you want to hit all of the bands exactly. If not a lightning strike, I will write an article about the experience as well. My question is what is 'higher frequency' specifically? = 1/30.e6 = 33 nS. Frank VK1VK. Basu Bhattacharya (VU2NSB). If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. I dont have an amplifier, so only need to be able to handle 100W. When I'm measuring the half way point on my EFHW, looking for 67', how do I factor in the compensation coil on the MyAntennas wire? What seemed to work best was to concentrate the turns on the tap-side of the secondary winding, using several (#28) wires in parallel for the primary turns such that they covered about half of the underlying secondary winding. For . I would mention first its ease of installation. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. Change). The original coil is designed for low power portable applications. The technical storage or access that is used exclusively for anonymous statistical purposes. I did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. I assume you know the GNARC source for EFHW antennas. I set up an EFHW for field day using a similar transformer with 25 ft. of coax from the box, everything floating, to my battery powered radio. This will also be handling 100W. Krem, rja le, mi a krdse. Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. BG7TBL FA-3-6G frequency meter initial impressions, tinyPFA HP8656B vs Trimble Thunderbolt GPSDO, tinyPFA Trimble Thunderbolt GPSDO vs Leo Bodnar Precision GPSDO, (tr)uSDX unauthorised product and countermeasures, Comparing RF Power Amplifier Tube Performance Computer and Calculate initial load line of valve RF amplifier on the AL811H, Review of inexpensive Chinese thermostat DST1000, Garden environmental telemetry project part 5, Another small efficient matching transformer for an EFHW 2643251002 #5 improved Simsmith model (v1.03), A Simsmith model of a Ruthroff 1:4 voltage balun 2843009902 (BN43-7051), Another small efficient matching transformer for an EFHW 2 x 5943000601 (FT82-43) VK4JJ build and measurement, Another small efficient matching transformer for an EFHW LO1238 VK3PY, VK3TU build and measurement, An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03), Modelling an antenna as a simple two terminal resistance is often naive, Garden environmental telemetry project part 4, A simple transformer model of the Guanella 1:4 balun some further observations, A simple transformer model of the Guanella 1:4 balun, An experimental propagation beacon on 144.385MHz part 2, An experimental propagation beacon on 144.385MHz, Another small efficient matching transformer for an EFHW 2643251002 #4 G8GYW build and measurement, Digital directional wattmeter based on G8GYW part 2, Garden environmental telemetry project part 3, Some wooly thinking on Antenna Factor online, Garden environmental telemetry project part 2, LED plate driver failure 24W round plate, Digital directional wattmeter based on G8GYW part 1, Diagnosis of a 9:1 transformer from NanoVNA plot part 2, Diagnosis of a 9:1 transformer from NanoVNA plot, Garden environmental telemetry project part 1, Digital display for DIY 25W dummy load part 4.